Generally, in the process for downmixing an audio signal including a plurality of objects into a mono or stereo signal, parameters are extracted from the objects. These parameters are usable in decoding a downmixed signal. And, a panning and gain of each of the objects are controllable by a selection made by a user as well as the parameters.
First of all, a panning and gain of objects included in a downmix signal can be controlled by a selection made by a user. However, in case that a user controls objects, it is inconvenient for the user to directly control all object signals. Compared to a case of control by an expert, it may be difficult to reproduce an optimal state of an audio signal including a plurality of objects.
Secondly, in case that a user adjusts pannings and gains of objects, it is necessary to determine whether an output signal is a stereo object signal. If the output signal is the stereo object signal, the stereo object signal should be controlled using one user input.